Note: Descriptions are shown in the official language in which they were submitted.
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FILMS, PACKAGING AND METHODS FOR MAKING THEM
This invention concerns films and packages produced therefrom which include
means for
facilitating their opening and/or applying line(s) and/or patterns thereto, as
well as methods for
producing such films.
Flexible polymeric films are widely used as packaging materials for a vast
range of goods..
Furthermore, a variety of synthetic polymers are used for producing such
packaging materials,
for example films made from synthetic polymers, such as (polyolefins [e.g.
polyethylene and/or,
polypropylene] polystyrene and/or polyesters) and/or natural polymers (such as
cellulosic
materials and/or biopolymers e.g. polylactic acid).
One particular packaging use for such films is as an overwrap for a variety of
goods, for
example for cigarette packets, video tapes, cookies etc., the films being
sealed tightly over the
goods. However, the very properties which confer desirable properties on the
films as
packaging materials, for example high strength and tear resistance,-make such
packages
difficult to open because the films of which they are made are difficult to
tear.
In order to facilitate the opening of such packages, so-called "tear tapes"
have been provided
which consist of a narrow strip of a polymeric film adhered to internal
surface of the packaging
film, a tab of the tear tape being left free on the outside of package to
facilitate its opening. The
package can then be opened by pulling the tear tape through the packaging
film.
Although tear tapes can be a good and efficient way of opening such packages,
applying the
tape to the packaging film adds to the total cost of the packages. Furthermore
it can still be
difficult to open such packages as the end of the tape is often difficult to
find. Therefore it has
been proposed instead to provide inherent in the film other means of opening a
pack, such as
one or more lines of weakness on the film. Two lines are generally preferred
to define a film
strip of sufficient width to enable ease of grasping, removal and hence
opening of the pack.
It has previously been known to use lasers to ablate and/or burn off a
thickness of film to create
a line of weakness along which the film can be torn. For example such
techniques are
described in US 3,909,582; US 5,630,308 (both American Can). US 5,010,325 and
US
5,010,231 (both LPF) describe methods which use a laser which can be tuned to
emit a given
wavelength to better match the incident radiation to the film being scored.
However such
tunable lasers remain only research tools which are not available commercially
making such a
technique impractical on an industrial scale as weli as very expensive. It is
also known to use a
laser or other means to create a line of perforations in a film (e.g. where a
laser removes at
various points along the film either the whole thickness through of the film
to form a hole or
some substantial proportion of material to form a well or indent in the film
surface). Such
CONFIRMATION COPY
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2
perforations may also act as a tear line to aid opening of a pack wrapped in
such a film.
The prior art methods of using lasers to score and/or perforate film have many
disadvantages.
The laser actually removes a layer of film thickness to weaken the film. Thus
upper coats or
layers are removed which can adversely effect other film properties in the
treated area (e.g.
water vapour and/or oxygen permeability). As the film surface is vaporised by
the laser,
potentially hazardous and/or noxious polymer vapour is produced which requires
expensive and,
complicated associated equipment to extract the fumes. It can be difficult to
control the laser
position so that it only cuts through a partial sectiori of an already very
thin film.
Furthermore physically removing significant amounts of material from the film
surface can lead
to another major disadvantage. Firstly the weakened line is thinner than the
surrounding film
which creates a furrow in the film surface. Secondly during laser ablation
large amounts of film
material are thrown up either side of the score line which then condenses onto
the film
alongside the line. Melting of the film may also cause film polymer to flow
across the film
surface adjacent to the line. Both these effects tend to form ridges parallel
to and either side of
each score line. Thus tear lines made by prior art methods have pronounced
furrows and
ridges when the film is see in cross-section (e.g. see Figure 2 herein).
Such an uneven cross-sectional profile whilst not necessarily readily seen by
the unaided naked
eye on a single sheet can nevertheless cause problems when a film is wound
onto large reels
to form rolls of film comprising many thousands of sheets of film laid on top
of one another:
Industrial sized rolls of prior art film with such laser scored tear lines
show very pronounced
ridges and furrows around the outer surface of the roll (e.g. see Figure 3
herein). These
correspond to the cumulative effect of the underlying ridges and furrows of
the tear lines in
each film sheet and have many undesirable effects. It is difficult to use such
rolls in
applications requiring precise positioning of the film web. The ridges and
furrows provide an
uneven surface for further coating, finishing and printing. The film is also
stretched over the
ridged areas when wound around a reel which can create undesired physical
changes in these
areas as some film properties such as heat shrink and optical properties are
altered by
stretching. For applications such as over-wrapping where the film is heat
shrunk around a pack
(e.g. tobacco product), any differential stretching in the film can lead to
disadvantages such as
areas of looseness around the pack; an imperfect seal; areas of variable
opacity and/or an
unsightly pack. Thus current laser scored tearable films exhibit unevenness to
an extent which
is unacceptable when the film is wound onto a roll.
It would be desirable to find a method of providing a means more readily to
tear a film which is
integral to the film and which eliminates or reduces some or all of the
preceding disadvantages
with prior art films.
The applicant has surprisingly discovered that tear susceptible line(s) and/or
pattern(s) can be
CA 02434074 2009-04-15
3
created in an film without creating large unevenness in the film gauge.
Line(s) and/or pattern(s)
in the film can also be created which have other uses as well as, or instead
of, to facilitate
tearing of the film.
Therefore according to the present invention there is provided a flexible,
oriented
polymeric, film having a thickness of from 10 to 120 pm and having at least
one tear
susceptible line(s) and/or pattern(s) thereon, wherein the film material
within the
line(s) and/or patterns) has a substantially improved, enhanced or redirected
orientation to material in the rest of the film, the line(s) and/or pattern(s)
lines having
substantially the same gauge as the rest of the film, and the line(s) and/or
pattern(s)
being formed by a direct chemical and/or radiation treatment which removes
substantially no material from the film.
As used herein differences in orientation between two compared regions of film
may
denote a difference in the extent of orientation (such as degree of order in
the film
material(s)) and/or difference(s) in the direction(s) of orientation (such as
alignment(s) of film material(s), for example polymer chains and/or crystals)
within
the film. Preferably, the material in the line(s) and/or pattern(s) may be
substantially
more oriented in extent and/or direction that the material in the rest of the
film.
Preferably the line(s) and/or pattern(s) lines have substantially the same
gauge as
the rest of the film.
Preferably the film tears substantially along the line(s) and/or pattern(s)
when tearing is initiated
therealong. However it will be appreciated that if the difference in
orientation between the
material within the line(s) and/or pattern(s) and the material in the rest of
the film is insufficient
to facilitate ready tearing therealong, such line(s) and/or pattern(s) may
nevertheless be
created thereon for other purposes such as to create aesthetic and/or other
properties
therealong. For example the film material therealong may be made more
susceptible and/or
resistant to future treatment(s) of and/or coating(s) on the film and/or the
visual appearance of
the film therealong may be selectively altered e.g. due to changes in opacity,
different
wavelengths scattered etc.
CA 02434074 2009-04-15
4
In another aspect of the present invention there is provided a flexible
optionally polymeric film
having at least one tear susceptible line(s) and/or pattern(s) thereon
characterised in that the
line(s) and/or pattern(s) lines have substantially the same gauge as the rest
of the film.
As used herein tear susceptible line(s) and/or pattern(s) refer to line(s)
and/or pattern(s) on the
film which preferentially tear therealong due to the properties of the film
therealong compared
to the rest of the film. For example a tear susceptible line or pattern may
comprise material
which is mechanically weaker (e.g. due to treatment) than the material in the
rest of the film.
Preferably the film material within the tear susceptible line(s) and/or
pattern(s) has a
substantially different orientation to material in the rest of the film.
More preferred films are those which the material in the line(s) and/or
pattern(s) has a
substantially different orientation to material in the rest of the film and
the line(s) and/or
pattern(s) have substantially the same gauge as the rest of the film.
As used herein gauge denotes the mean thickness of a film (or specified region
of film)
measured normal to the film surface.
Preferred films of the invention comprise line(s) and/or patterns(s) that are
substantially free
from ridges (or comprises only very small ridges) along the edges thereof
compared to the
substantial ridges seen along the edges of tear lines of prior art films. Tear
susceptible line(s)
and/or pattern(s) prepared as described herein optionally exhibit less
mechanicar strength (i.e.
weakness) in the direction of the line without removing significant amounts of
material
therealong. As little or no material is removed then very little if any
furrowing is seen and any
surface coatings can remain largely intact. As large volumes of polymer fumes
are not
generated there is also no need for extraction equipment. Thus the method of
the present
invention can be used using readily available equipment and without requiring
extensive
modification to conventional production lines for film webs.
In one embodiment of the present invention it has been surprisingly found that
line(s) and/or
patterns (optionally tear susceptible) can be created in an oriented
thermoplastic polymer film
by focussing onto the web a conventional CO2 laser at low power levels
insufficient to ablate
polymer from the surface. Without wishing to be bound by any mechanism it is
also believed
that the laser has sufficient power to heat the film along the line and alter
the orientation of the
polymer chains therein (for example increasing orientation in the direction in
which the laser is
applied e.g. MD). It is also observed that if the film web stays substantially
within a region close
to the laser focal plane sufficient change in orientation will occur to create
an effective tear
CA 02434074 2009-04-15
4a
susceptible line. There is a reasonable tolerance permitted in the relative
positioning of the
laser with respect to the film web, which is useful when dealing with web
"chatter" where the
plane of the film web is displaced by small amounts normal to the film surface
as the web
passes through the machine. This compares favourably to prior art methods of
laser scoring
where the positioning of the laser beam relative to the web is much more
critical if one is to
remove material from only a part of the thickness of an already very thin
film.
Preferred films of the invention comprise oriented material, more preferably
oriented polymeric
material and most preferably biaxially oriented polymer. Preferably the
material comprising the
line(s) and/or pattern(s) herein is substantially more oriented than that the
optionally oriented
material comprising the rest of the film. More preferably the film material
therealong is more
oriented in one direction (e.g. MD) compared to the material in the rest of
the film. Alternatively
the line(s) and/or pattern(s) herein may be less oriented the rest of the
film, for example
comprise substantially randomly and/or unoriented material.
According to one preferred embodiment, the line(s) and/or pattern(s) thereon
are
formed by a directed treatment selected from irradiation through patterned
lithographic masks, positioning of a chemical along the line, focussed
electromagnetic radiation, focussed particulate radiation and combination of
at least
two of them.
According to another preferred embodiment the line(s) and/or pattern(s) are
formed
by ink-jet printing, chemical treatment or coating onto the films.
It will also be appreciated that the line(s) and/or pattern(s) as described in
the present invention
herein may comprise in whole or in part regions which are substantially
continuous. Preferably
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the line(s) and/or pattern(s) herein exist substantially across the full the
width of the film for
example as measured in the transverse direction (TD) if the line(s) and/or
pattern(s) herein are
created in substantially in the MD. However the line(s) and/or pattern(s)
herein may also
comprise in whole and/or in part, regions which are substantially
discontinuous. More
preferably there may comprise at regular intervals a plurality of spots and/or
dashes of film
having material whose orientation has been altered therein such that the
line(s) and/or
pattern(s) herein is delineated on the film. Continuous line(s) and/or
pattern(s) could for,
example be formed by a continuous and/or a pulsed laser with a high pulse
frequency.
Discontinuous line(s) and/or pattern(s) could for example be formed by a
pulsed laser where
the pulse frequency is suitably matched to the speed at which the film web
moves past the
laser.
The invention herein preferably comprises line(s), region(s) and/or pattern(s)
which are tear
susceptible (e.g. weakened) and therefore especially useful as a tear guide
for opening the film
and/or for removing a defined region of film to create a shaped opening
therein. However as
well as, or optionally instead of, this tear susceptibility, suitable means
(such as a laser at very
low power) may also be used to define line(s), region(s) and/or pattern(s) on
the film which are
more or less susceptible to other subsequent treatments thereof and/or
coatings and/or layers
thereon. For example coatings may differentially adhere (or not adhere) to the
treated region(s)
compared to the rest of the film. This allows formation of line(s) and/or
pattern(s) on the film
with many different properties.
The invention further provides a method for creating, in a flexible optionally
polymeric film, at
least one line and/or pattern thereon so the film will tear substantially
along the line(s) and/or
pattern(s) when tearing is initiated therealong; characterised in that the
method comprises the
step of: directing onto a web of film a means to make the line(s) and/or
pattern(s) susceptible to
being torn therealong without removing significant amounts of material
therefrom so the line(s)
and/or pattern(s) have substantially the same gauge as the rest of the film.
Another aspect of the invention provides a method for creating, in a flexible
optionally polymeric
film, at least one line and/or pattern thereon so the film along the line(s)
and/or pattern(s) is
susceptible or resIstant to further treatment; characterised in that the
method comprises the
step of directing onto a web of the film a means to differentially to orient
material along the
line(s) and/or pattern(s) so the material therealong has a substantially
different orientation
(optionally is more ordered) than material in the rest of the film and the
line(s) and/or pattern(s)
have substantially the same gauge as the rest of the film.
A still further aspect of the invention provides a method for creating, in a
flexible optionally
polymeric film, at least one line and/or pattern thereon so the film will tear
substantially along
the line(s) and/or pattern(s) when tearing is initiated therealong;
characterised in that the
method comprises the step(s) of:
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(a) directing onto a web of the film a means differentially to orient material
along the line(s)
and/or pattern(s) so the material therealong has a substantially different
orientation (optionally
is more ordered) than material in the rest of the film; and/or
(b) directing onto a web of film a means to make the line(s) and/or pattern(s)
susceptible to
tearing therealong without removing significant amounts of material therefrom
so the line or
lines have substantially the same gauge as the rest of the film.
In a preferred method of the invention steps (a) and (b) are simultaneous
rather than
sequential; and more preferably the differential orienting means of (a) and
the tear susceptibility
means of (b) and are the same means (i.e. one method achieves both effects).
It will be appreciated that when determining whether any change has occurred
in the film gauge
along the line(s) and/or pattern(s) herein (e.g. created as described) many
criteria should be
considered. For example one could assess just the thickness of the line itself
(the degree of
furrowing) and/or one could look at the boundary region between the line and
the rest of the
bulk film as this is where undesirably large ridges may form. Thus preferred
films of the
present invention may exhibit reduced (more preferably substantially no)
furrows (thinning in the
line itself) and/or reduced (more preferably substantially no) ridges (peaks
either side of the
line). Most preferred films show a effect in reducing and/or eliminating both
the ridge and the
furrow not just one of them. More preferred films of the invention will have a
substantially flush
cross-section (i.e. a substantially uniform gauge across the whole width of
the film) taking into
account normal variability in gauge due unavoidably to the nature of
conventional processes
used to form films and ignoring the extreme edges of the web (where for
example stenter clips
may be attached) as these edges may well be trimmed from the final film. It
will also be
appreciated that ridges and furrows may be manifest on one or both sides of
the film surface.
However it is a preferred advantage of the films of the present invention that
if present as well
as being small ridges and furrows tend to occur on one side of the film only,
generally the side
of the film incident to the means used to generate the line or lines. Prior
art methods for
producing tear lines lead to films having much larger ridges and furrows which
generally occur
on both sides of the film.
Any suitable mearis to increase the order (i.e. reduce the entropy and/or
increase orientation) of
the film material along the line(s) and/or pattern(s) herein may be used.
Alternatively
orientation can be scrambled, reduced and/or randomised along the line to also
create a line of
discontinuity (phase change) which may also act as a tear susceptible line if
required and/or
make the line(s) and/or pattern(s) differentially susceptible or resistant to
further treatment(s),
layer(s) and/or coating(s). Such means may comprise for example focussed
chemical or
radiation treatment (e.g. heat) such as an infra-red laser. Conveniently a
standard industrial
C02 laser of wavelength 10.6 microns (1 micron = 1 N= 1 pm = 1 x 10'6 m) may
used as this is
4o readily available. Although for certain common film materials such as
polypropylene the
wavelength of a CO2 laser is not readily adsorbed as the process of the
present invention
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requires very low levels of power a standard mass produced CO2 laser is more
than adequate.
Thus it is an advantage of one embodiment of this invention that such cheap
and readily
available lasers can be used. However it will be appreciated that in the
method of the present
invention any suitable lasers of other more optimal wavelength(s) for the film
material may be
used (and/or tuneable lasers) as and when such lasers become more commercially
available at
a reasonable cost. If treatment and/or creation of the line(s) and/or
pattern(s) herein is by laser
it is at a power insufficient to remove film material (e.g. by ablation).
Alternatively a method of the present invention comprises the step of/
directing onto at least one line and/or pattern selected on a web of a
polymeric film oriented in
at least one (preferably two) direction(s), a tear susceptibility means which
selectively alters
(preferably increases) film orientation along the line(s) and/or pattern(s)
but not in the rest of
the film; such that the tear susceptibility means does not remove significant
amounts of film
thereform;
to form in the resultant film tear susceptible line(s) and/or pattern(s)
thereon having
substantially the same gauge therealong as the rest of the film.
Alternatively a method of the present invention comprises the steps of
(i) directing onto at least one line and/or pattern selected on a web of a
flexible,
substantially unoriented polymeric film, a tear susceptibility means which
selectively inhibits or
substantially prevents film orientation along the line(s) and/or pattern(s)
but not in the rest of the
film; such that the tear susceptibility means does not remove significant
amounts of film
thereform; and
(ii) subsequently orienting the rest of the film such that the film remains
substantially non-
oriented or less oriented along the line(s) and/or pattern(s),
to form in the resultant film tear susceptible line(s) and/or pattern(s)
thereon having
substantially the same gauge therealong as the rest of the film.
Any suitable means to inhibit or prevent orientation as required may be used.
A physical barrier
such as a mask and/or coating may be used to block or inhibit subsequent
treatment to orient
the rest of the film and/or make the film more susceptible to subsequent
orientation.
Alternatively or as~well, the selected line and/or pattern on the film can be
treated to make the
film therealong more resistant to subsequent orientation.
The treatments used to create the line(s) and/or pattern(s) on films of the
invention, can by
applied by suitable directable means such as, patterned lithographic masks,
jets (for example
coatings or chemical treatments applied by ink jet printer) and/or by
radiation (for example
electromagnetic e.g. {R, visible, UV and/or particulate e.g. electron beam
[EB]). The treatments
which may be used can be those which act directly to alter (e.g. improve,
scramble or
randomise) orientation in the treated area (e.g. by use of heat, preferably
focused laser beam).
Alternatively, or as well, the treatments may act to inhibit or enhance
subsequent orientation of
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film material in the selectively treated area (e.g. by cross-linking or
denaturing the film
polymer). Preferably the treatment parameters should be set so that the tear
susceptible line(s)
and/or pattern(s) in the final=film have substantially the same thickness
(gauge) as the rest of
the film. More preferably the tear susceptible line(s) and/or pattern(s) are
weaker than the rest
of the film.
The advantage of using a focussed laser directed normally to the film surface
is that as the size,
of the focal beam is comparable to or less than the thickness of the a typical
film web through
which the laser beam passes, the properties of the film are effected (i.e.
polymer chain
orientation is altered) simultaneously throughout the film thickness within
the selected line(s)
and/or pattern(s) not just the on the surface. The use of a laser to create a
very narrow line
minimises any effect on the overall performance of the piece of film used.
This also permits
some greater degree of tolerance in positioning of the film web in a plane
normal to the incident
laser beam (e.g. some flexing of the film can occur) without substantially
effecting the alteration
of polymer orientation within the selected line(s) and/or pattern(s).
It is preferred to improve, enhance or re-direct orientation of polymer chains
along line(s) and/or
pattern(s) on a film which has previously been oriented as this is less likely
to produce handling
problems than selectively orienting material along the line(s) and/or
pattern(s), especially if
orientation achieved by stretching, as otherwise the film may break or tear
during processing.
However if film orientation can be achieved by some other method which
requires less film
handing (such a chemical or radiation treatment) it may then' be practical to
enhance orientation
along the line(s) and/or pattern(s) herein by selectively orienting the
material therealong before
optionally orienting the rest of the film.
Because substantially no material has been removed from the line(s) and/or
pattern(s) herein,
they are substantially unridged (i.e. have a substantially flat, non-furrowed
profile flush with the
film surface when seen in cross-section through the film). Such line(s) and/or
pattern(s) can be
formed by any suitable means (such as those described herein) preferably where
the material
in the line(s) and/or pattern(s) is more oriented than that in the rest of the
film.
Films of the invention may be tested by any suitable method to measure the
degree of and the
direction(s) of orientation within the line(s) and/or pattern(s) herein, for
example polarimetry
and/or Raman spectroscopy. Preferably the line(s) and/or pattern(s) herein are
sufficiently
differently oriented, more preferably more oriented, compared to the rest of
the film that such a
difference can be detected by at least one of these suitable methods.
Another aspect of the invention provides a package comprising at least one
article wrapped in a
flexible oriented polymeric film of the invention.
Another aspect of the invention provides at least one article wrapped in a
flexible oriented
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polymeric film of the invention.
Once the film has been sealed around the article, tearing of the film
substantially along a tear
susceptible line and/or pattern preferably occurs with peeling of the seal.
The film can be heat
or cold sealed around the article.'
The film of packages of the present invention can be printed, and this
preferably includes an;
indication of the position for initiating tearing of the film to open them.
If the line(s) and/or pattern(s) herein are tear susceptible it is preferred
that the at least one of
the line (s) and/or pattern(s) extend to the edge of the film on the package
to assist tearing
therealong. However, there can also be an advantage in having a cut extending
from the edge
of the film to assist in the initiation of a tear along the line(s) and/or
pattern(s) herein.
Packages in accordance with the present invention can be opened easily in a
similar manner to
those using separately applied tear tapes, but the need for such tear tapes is
avoided.
Although a single tear susceptible line can be used, so that the package can
be opened by
tearing it open substantially along this line, it is generally preferred for
packages of the present
invention to include at least a pair of such lines. Optionally the pair of
lines are substantially
mutually parallel and define a strip of film, which can be torn away from the
rest of the film,
much in the manner in which packages having a tear tape are opened but without
the necessity
for having such a tape.
When more than one tear susceptible line is used, the distance between the
individual lines is
not limited by the cost considerations which apply when separate tear tapes
are used because
tearing of films and packages in accordance with the present invention can be
effected without
the use of such tapes. However, it is generally preferred that when two lines
are used they be
at least about one mm apart in order to facilitate being able physically to
take hold of the end of
the edge of the film when the package is to be opened and also to minimise the
risk that tearing
transfers from the two lines into only one when the package is opened. As will
be appreciated,
an unsealed tab extending from the edge of the film on the package will
usually make this
easier. However, the lines can be spaced considerably further apart, for
example about 10 mm
apart or more, but a preferred distance apart is in the range of from about 2
to about 6 mm.
It has been proposed hitherto to use coloured tear tapes in order to
facilitate being able to see
the end of the tape and thereby opening of the packages. The present invention
achieves
tearing open of the packages without the necessity of a tear tape, and so in a
preferred
embodiment of the present invention at least a portion of the film between a
plurality (preferably
two) tear susceptible lines and/or patterns herein is coloured, for example a
coloured tear tab
can be used rather than colouring the whole of the region of the film
therebetween. Other
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suitable means could be used to indicate the position of the lines and/or
patterns for example
the means used to form them could be adjusted (or intrinsically) alter the
optical properties of
the film therealong; and/or in sequence or in parallel another method could be
used to mark
one or more region(s) defined between the plurality of lines and/or patterns.
5
As will be appreciated, to open a package by tearing along the tear
susceptible line(s) and/or
pattern(s) herein, generally requires a tear to be initiated from an exposed
edge of the film.,
This can be achieved by leaving an at least partially unsealed region at the
edge of the film,
and this is preferably achieved'using a tab extending from one edge of the
film. "Although the
1o line(s) and/or pattern(s) herein preferably extend to the edge of the film,
tearing can start some
distance from the edge of the film, for example by providing a slit or notch
(e.g. V or U shaped)
in the edge of the film which extends towards and possibly into the line(s)
and/or pattern(s).
The (optionally very narrow) lines herein do not involve perforation of the
film as this could
seriously reduce the barrier properties of the film. Unlike prior art methods
the film can be
treated along line(s) and/or pattern(s) in a manner sufficient to facilitate
tearing therealong
without reducing the thickness of the film at all or to any great extent.
Various methods as
described herein can be used to effect the tear susceptibility of the film
(e.g. by selective
weakening) without substantial thinning, if 'any. Preferred methods can
involve non contact
(e.g. thermal) and/or mechanical means which cause either more orientation
along the line(s)
and/or pattern(s) or conversely less orientation in the rest of the film. The
line(s) and/or
pattern(s) herein can be continuous or discontinuous, but when they are
discontinuous they
should still be such that a tear once started will propagate essentially along
the line(s) and/or
pattern(s) and thus move from one treated (e.g. weakened) section to the next.
It is generally preferred that the tear susceptibility arises because after
treatment (e.g. as
described herein) material comprising the line(s) and/or pattern(s) is weaker
(e.g. has a lower
tensile strength) than the material comprising the surrounding film.
An example of a non contact means for forming the line(s) and/or pattern(s)
herein is the a non
ablative laser which treats the film therealong. An example of a mechanical
means is a suitably
controlled blade or roller which applies pressure to the film surface. These
means neither
puncture the film nor remove substantial amounts of material therefrom. It is
believed that they
act entirely or mainly by altering orientation of the film material within the
treated line(s) and/or
pattern(s) as the film therealong is subjected to, respectively, -heat or
mechanical pressure.
Lasers of suitable power have enabled a particularly good tearing to be
achieved along the
lines of laser treatment. However, using blades to apply pressure can also
provide satisfactory
results, as can a roller working in an appropriately shaped groove. An
advantage of using
lasers compared with methods such as blades and/or grooved rollers is that the
properties of
the treated line (e.g. degree of orientation change and/or weakening) is
usually relatively easy
to control by adjustment of laser settings (such as power and position of the
focal plane)
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11 ,
whereas the mechanical tolerances required to produce changes in line(s)
and/or pattern(s) by
mechanical means are often more difficult to control, especially as it is
desired that substantially
no film material is to be removed by the treatment.
The direction of the line(s) and%or pattern(s) herein relative to the film
itself is in general
unimportant, particularly with films having balanced properties. However, it
is usually
convenient to make these line(s) and/or pattern(s) along the direction in
which the film is,
manufactured (MD), and this can be particularly conveniently effected during
operations
subsequent to _the film production process, for example during slitting of a
larger rolls of film to
produce reels of film which are to be used on a packaging machine.
It is also possible to create line(s) and/or pattern(s) herein in any
configuration (especially with a
laser or ink-jet printer head). For example line(s) and/or pattern(s) herein
that are tear
susceptible can be created on the film to define regions and shapes which can
be readily cut,
torn, pressed out, or otherwise removed and or separated (in whole of in part)
by the end user.
The tear susceptible line(s) and/or pattern(s) herein have applications in
other areas, not just
packaging, for example to create complicated film shapes and patterns,
security features; tear
susceptible lines for books of documents (such as tickets) etc.
2o The film and/or sheet in which line(s) and/or pattern(s) herein are
introduced according to the
present invention may be any suitable substrate, such as any well known
sheeting material(s),
preferably the rimaterial of which can be oriented in at least one direction
and therefore also de-
oriented along a line thereon. Suitable sheeting materials may comprise any of
the following:
paper, synthetic paper, woven fabric, non-woven fabric, ceramic sheet,
metallic fibre sheet,
metallised sheet or film, metallic foil, metallic plate; films made from
organic polymers,
preferably biopolymers, more preferably films made from one or more suitable
carbohydrates;
polysaccharides (such as starch, celiulose, glycogen, hemi-cellulose, chitin,
fructan inulin; lignin
and/or pectic substances); gums; proteins, optionally cereal, vegetable and/or
animal proteins
(such as gluten [e.g. from wheat], whey protein, and/or gelatin); colloids
(such as hydro-
colloids, for example natural hydrocolloids, e.g. gums); polylactic,
polygalactic and/or cellulosic
films (e.g. microbal and/or regenerated cellulose film)]; thermoplastic films;
polymeric films (for
example films cornprising: polyolefins [e.g. polypropylene and/or
polyethylene] polyurethanes,
polyvinylhalides [e.g. PVC], polyesters [e.g. polyethylene terephthalate -
PET], polyamides [e.g.
nylons] and/or non-hydrocarbon polymers); and/or multilayer and/or composite
sheets formed
by any suitable combinations and/or mixtures of thereof.
It will be appreciated that in the end any sheet substrate can be used to form
a sheet of the
present invention provided that line(s) and/or pattern(s) herein can be
introduced thereto
without significant removal of material from the sheet such that the
disadvantageous ridge and
furrow effects in a tear susceptible line or pattern (e.g. line or pattern of
weakening) can be
avoided or substantially eliminated. Thus preferred sheet substrates are those
in which
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differential orientation can be introduced between the bulk of the sheet and
the line(s) and/or
pattern(s) herein. More preferred sheets are those which comprise constituent
materials which
can initially be substantially oriented in one or more directions along the
sheet and then
subsequently wholly or partially re-oriented by action of a suitable means
such as a laser along
a line on the sheet to create line(s) and/or pattern(s) herein without
significant removal of
material.
Preferred films of the present invention may be produced from a variety of
synthetic polymers,
for example may be polyolefin based films, e.g. polyethylene based,
polypropyl"ene based or
made from polystyrene, or they may be polyester based films. Furthermore,
films of the
present invention may be in the form of monolayers of a particular polymer,
although preferred
films comprise two or more layers which can be formed by coextrusion and/or by
coating.
The films are preferably heat sealable, and it is generally preferred that
when they have been
heat sealed the heat seals themselves have peel strengths less than the force
required to tear
the film along line(s) and/or pattern(s) herein in order to facilitate
propagation of these tears
through the heat seal and then into non-sealed regions of the film around the
packaged articles.
If desired, cold seals can be used to seal the packages, and again it is
preferred that such
seals should peel to allow tearing along line(s) and/or pattern(s) herein to
propagate through
these seals.
Biaxially oriented polypropylene (BOPP) films are preferred for producing
sheets, films and/or
packages in accordance with the present invention. It is more preferred that
the BOPP films
have substantially balanced physical properties, for example as can be
produced using
substantially equal machine direction and transverse direction stretch ratios.
Although
sequential stretching can be used, in which heated rollers effect stretching
of the film in the
machine direction and a stenter oven is thereafter used to effect stretching
in the transverse
direction, it is generally preferred to use biaxially oriented films which
have been produced by
simultaneous stretching, for example using the so-called double bubble process
or a
simultaneous draw stenter. The machine direction and transverse direction
stretch ratios are
preferably in the range of from 4:1 to 10:1, and more preferably from 6:1 to
8:1.
The films used in accordance with the present invention can be of a variety of
thicknesses
according to the requirements of the packages which are to be produced. For
example they
can be from about 10 to about 120 microns thick, and preferably from about 14
to about 40
microns thick.
The tear susceptible iine(s) and/or pattern(s) formed herein should exhibit
properties (e.g. a
degree of weakening therealong) which are sufficient to enable a tear once
started to
propagate substantially along the line(s) and/or pattern(s) in which it has
started without
substantial deviation therefrom. Insufficient tear susceptibility will make it
difficult if not
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13
impossible to starting a tear therealong. However excessive tear
susceptibility (e.g. too much
weakening) could result in unwanted opening of the packages during normal
handling. As will
be appreciated by those skilled in the art, different methods of achieving
tear susceptibility of
the films can result in different tearability.
Although packages in accordance with the invention can be opened by tearing
the films
substantially along tear susceptible line(s) and/or pattern(s) in the
packaging film without the,
use of a tear tape, a tear tape can be used in conjunction with one or more
such line(s) and/or
pattern(s), for example to facilitate the tearing of films which are otherwise
difficult to open with
a tear tape, e.g. with particularly thick films or films made of polymers
which are inherently
resistant to tearing.
Unless the context indicates otherwise, the terms `effective' and/or
`suitable' as used herein (for
example with reference to the sheets, films, coatings, formulations, process,
methods, uses,
applications, products, materials, additives, compounds, monomers, oligomers,
polymer
precursors, polymers and/or resins described herein and/or used in, added to
and/or
incorporated in the present invention) will be understood to refer to those
components which if
used in the correct manner provide the required properties (such as an
improved tear tape
replacement film) to the present invention as described herein.
It will also be understood that any optional substituents that may be present
on any repeat unit
in any polymer described herein may be selected to improve the compatibility
thereof with any
other materials with which they may be formulated and/or incorporated to form
the invention
herein. Thus, the size and length of substituents may be selected to optimise
the physical
entanglement or interlocation with the resin or they may or may not comprise
other reactive
entities capable of chemically reacting and/or cross-linking with such resins.
Certain moieties, species, groups, repeat units, compounds, oligomers,
polymers, materials,
mixtures, compositions and/or formulations which comprise some or all of the
invention as
described herein may exist as one or more stereoisomers (such as enantiomers,
diastereoisomers, geometric isomers, tautomers and/or conformers), salts,
zwitterions,
complexes (such as chelates, clathrates, crown compounds, cyptands /
cryptades, inclusion
compounds, intercalation compounds, interstitial compounds, ligand complexes,
non-
stoichiometric complexes, organometallic complexes, Tr-adducts, solvates
and/or hydrates);
isotopically substituted forms, polymeric configurations [such as homo or
copolymers, random,
graft or block polymers, linear or branched polymers (e.g. star and/or side
branched polymers),
hyperbranched polymers and/or dendritic macromolecules (such as those of the
type described
in WO 93/17060), cross-linked and/or networked polymers, polymers obtainable
from di and/or
tri-valent repeat units, dendrimers, polymers of different tacticity (e.g.
isotactic, syndiotactic or
atactic polymers)]; polymorphs [such as interstitial forms, crystalline forms,
amorphous forms,
phases and/or solid solutions] combinations thereof where possible and/or
mixtures thereof.
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The sheets of the present invention comprise and/or incorporates all such
forms which are
effective and/or suitable.
It is appreciated that certain features of the invention, which are for -
clarity described in the
context of separate embodiments may also be provided in combination in a
single embodiment.
Conversely various features of the invention, which are for brevity, described
in the context of a
single embodiment, may also be provided separately and/or in any suitable sub-
combination.
The term "comprising" as used herein will be understood to mean that the list
following is non-
exhaustive and may or may not include any other additional suitable items, for
example one or
more further feature(s), component(s), ingredient(s) and/or substituent(s) as
appropriate.
Further and/or alternative features of the present invention are described in
the claims.
Embodiments of films and a packs according to the present invention will now
be described by
way of example with reference to the accompanying drawings. Features in each
drawing are
given number labels with the numbering in each drawing starting at the next
hundred (i.e. 1,
101, 201 etc). Similar and/or analogous features in each drawing are labelled
by numbers
separated by an whole number multiple of one hundred (e.g. features 1, 101 and
301 each
refer to the base film in Figures 1, 2 and 4 respectively).
Figure 1 is a section through a prior art packaging film with adhered tear
tape.
Figure 2 is a section through a prior art packaging film with tear susceptible
lines thereon
having a ridge and furrow cross-section made using a prior art laser ablation
method.
Figure 3 is a roll of the prior art film illustrated in Figure 2 which has
been wound onto a drum
showing a pronounced ridge of film on the surface of the film.
Figure 4 is a TD section through a tear open portion of one embodiment of a
film of the
invention where the tear line has been formed by a low powered laser and very
little material
has been removed from the film.
Figure 5 is a TD section through a tear open section of another embodiment of
a film of the
invention.
Figure 6 is a roll of the film of the invention illustrated in Figure 4 which
has been wound onto a
drum showing a substantially flat outer surface on the film roll.
Figure 7 shows a piece of film of Figure 4 shaped for overwrapping a cigarette
pack with a tab
for ease of pulling along a strip defined by two tear susceptible lines.
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Figure 8 is a perspective view of a cigarette pack overwrapped with the film
of Figure 4.
Figures 9 to 12 are photos of TD sections through films with tear susceptible
lines which
5 illustrate the difference between prior art laser scored films of Comp A
herein (Figures 9 and
10) and the films of Example 1 herein (Figures 11 and 12).
Figure 13 is a plot of intensity ratio (derived from Raman spectra as
described herein) across
the width of a tear susceptible line of the present invention in a PP film
showing the different PP
10 orientation within the line compared to the PP in the rest of the film.
Various embodiments of the present invention will now be described by way of
illustration only.
Referring to Figure 1, a heat sealable biaxially oriented polypropylene film
(1) has a separate
15 tear tape (3) adhered to a region (5) on the film (1) to form a line
thereon in the MD. A tab (not
shown) is attached to one end of the tear tape (3). When this film (1) is used
to overwrap a
cigarette pack (not shown) in a known manner the tear tape (3) is placed on
the inner surface
of the film (1). The tab is left free so when the tab is pulled, the tape (3)
tears through the film
(1) in regions (7) and (9) either side of the tape (3), to remove the strip of
film (5) to which the
tear tape (3) was attached. This enables the film (1) to be removed from the
pack and the pack
to be opened.
Figure 2 shows another prior art heat sealable biaxially oriented
polypropylene film (101) having
lines (107) and (109) scored in the film (101) in the MD using a laser
according to the prior art
methods. As indicated in Figure 2, the film (101) is of reduced thickness
along the scored lines
(107, 109) where material has been ablated by the laser beam, but it is of
increased thickness
on either side (111, 113) of these weakened lines (107, 109) where due to
removal of material,
ridge lines (111, 113) have formed. The portion (105) of the film (101)
between the scored
lines (107, 109) is of the same thickness as the rest of the film (101) as it
has not been directly
effected by the laser treatment. A tab (not shown) can similarly be attached
to region (105) of
the film and left free. Pulling the tab causes tearing to propagate along the
scored lines (107,
109) in the film (101) to remove a strip of film (105). Thus a pack
overwrapped with film (101)
can be opened as described in Figure 1.
Figure 3 shows a roll of film (215). A web of prior art film (201) as-shown in
Figure 2 is wound
around a drum in the MD to form a roll (215) of film in a conventional manner.
The portions of
film (201) of increased thickness (211, 213) either side of scored lines (207,
209) of reduced
thickness are cumulatively superimposed on top of each other in a large roll
(215) comprising
many hundreds of turns of film. Thus a pronounced ridges (211, 213) and
furrows (207, 209)
can be seen on the surface of this prior art roll (215) either side of the
strip of film (205). These
ridges (211, 213) and furrows (207, 209) are highly undesirable for the
reasons described
CA 02434074 2003-07-07
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herein as for example they can cause distortions and stretching in the filml).
Figures 4 shows one embodiment of a heat sealable biaxially oriented
polypropylene film of the
present invention (301) having tear susceptible lines (307, 309) produced
thereon which are
weaker than the rest of the filrri. (301). The lines were formed in the MD
using a laser
according to the method of the invention where only insignificant amount of
film material has
been removed. Unlike the prior art film shown in Figure 2, the film (301) is
of substantially ;
uniform thickness along the lines (307, 309) where the film material has been
treated by the
laser beam with only very small bumps (311, 313) seen either side of the lines
(307, 309).
lo Instead the orientation of the film (301) along lines (307, 309) has been
increased in the MD
due to the action of the heat of the laser beam. This increase in orientation
is indicated by the
shading of these regions (307, 309). The portion (305) of the film (301)
between the tear
susceptible weakened lines (307, 309) is of substantially the same thickness,
orientation and
strength as the rest of the film (301) as it has not been directly effected by
the laser treatment.
A tab (not shown) can similarly be attached to region (305) of the film and
left free. Pulling the
tab will cause a tear to propagate along the lines (307, 309) to remove a
strip of film (305) so
defined. Thus a pack overwrapped with film (301) can be opened in a similar
manner to that
described in Figure 1. It will also be appreciated that in another embodiment
of the invention
only one tear susceptible line [rather than the two lines (307, 309) shown in
Figure 4] need be
introduced in the film also to permit an overwrapped pack to be opened if a
suitable tab was
attached to the end of the single line.
Figure 5 shows another embodiment of a heat sealable biaxially oriented
polypropylene film of
the present invention (401) analogous to that shown in Figure 4 having lines
(407, 409)
produced in the film according to a method of the invention. However, unlike
the film in Figure
4, the orientation of the film (401) along lines (407, 409) has been scrambled
(randomised)
throughout the thickness of the film and this de-orientation is indicated by
the shading of these
regions (407, 409).
Figure 6 shows a web of the film (501) of Figure 4 wound around a drum in the
MD to form a
roll (515) of film in a conventional manner. The tear susceptible lines (507,
509) (formed as
described herein in the MD along the film) have substantially the same
thickness as the rest of
the film (501) and the strip of film (505) defined between the lines (507,
509). Thus when many
layers of film are cumulatively superimposed on top of each other in a large
roll (515)
comprising many hundreds of turns the outer surface of the roll remains
substantially even
because there are little or no ridges or furrows along the lines (507, 509).
Thus little or no
distortion or stretching of the film (501) is observed when the web is wound
onto the roll (515).
Figure 7 shows a film (601) of the invention as shown in cross-section in
Figure 4, which has
been shaped to be more readily useful in overwrapping a pack. Specifically a
notch (617) has
been provided at one end of the strip of film (605) between the two tear
susceptible lines (607,
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609) to allow for greater ease in initiating a tear along these lines as
described herein. It will be
appreciated that other suitable means could be also be used to aid tear
initiation therealong
such as a tab (619) shaped and/or attached to the region (605). In preferred
films of the
invention either one or both of a tab or notch may be used to aid tearing.
Figure 8 shows a cigarette pack (721) overwrapped with a film of the invention
(701) having a
tearable strip (705) thereon defined by the tear susceptible lines (707, 709)
and a tab (719),
attached to the strip (705) to aid removal thereof and hence unwrapping of the
film (701) from
the pack (721).
To illustrate and explain the invention the following non-limiting examples of
a film of the
invention and (as a comparison) a prior art film were prepared as follows:
BOPP Film
A three layer polymeric tube was formed by coextruding a core layer of
polypropylene (also as
referred to herein as PP) homopolymer with a layer of medium density
polyethylene on each
side of the core layer. The tube was cooled and subsequently re-heated before
being blown to
produce a three layer biaxially oriented polypropylene (also referred to
herein as BOPP) film
having a core layer which was 18.7pm thick and two outer layers which were
each 0.3pm thick,
the film itself being 19.3pm thick. Different methods were used to create tear
susceptible lines
on this conventional BOPP film.
Comp A
As a comparative example a single laser ablated line (107) was scored in the
machine direction
(MD) along a conventional BOPP film (101) prepared as described above using
the
conventional method of scoring with a high powered laser. Fumes of vaporised
PP were
observed where the laser beam hit the film (101) indicating that significant
amounts of PP was
being burnt from the surface of the film (101) as the weakened score line
(107) was being
formed.
Example 1
A web of a BOPP film (301) prepared as described above was fed at a speed of
200 ft per
minute past a 50 W C02 laser of wavelength 10.6 microns. The laser beam was
split into two
to reduce the power of the laser at the web to about 7W. A single laser beam
was focussed
onto the film web to heat the film (301) along a single line (307) in the MD
in a manner sufficient
to scramble the orientation of the PP therealong without burning off
significant amounts of the
polymer. The result was a weakened line (307) on the film (301) which could be
torn
therealong by hand pressure. It was found that for this laser power settings
of between about
40% and about 65% produced usable tears in the film. If the power was too high
material
began to be ablated from the film surface and if too low the laser power did
not scramble film
orientation sufficiently to produce enough weakening for an easy tear. The
aforementioned
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films (301) were produced with a pair of tear susceptible lines (307, 309)
thereon and such films
could be wound up onto large reels without noticeable ridging thereon.
Results
Referring to Figures 9 to 12 herein, photographs of various prior art films
and films of the
present invention were taken under magnification. The film was sandwiched
between a
suitable embedding material and sliced in the TD to allow a cross-section
through the film to be,
seen.
Figure 9 is a photograph taken under normal transmitted light of the prior art
BOPP film Comp
A (801) sandwiched within an embedding material (823). A scale bar (825) 100
microns in
length superimposed on the photograph to indicate the degree of magnification
of the image.
On one side there is an air gap (827) between the film and the embedding
material.
Pronounced ridges and furrows can be seen at both the top and bottom surfaces
of the film
along the laser scored line of weakening (807) and there is significant
thinning of the film
therealong.
Figure 10 is a photograph taken under transmitted cross polarised light of the
same sample of
Comp A at the same magnification (where 925 denotes a scale bar also 100
microns long).
The orientation of material within the film (901) and the tear susceptible
line (907) can be seen
as largely the same, as the line (907) appears grey and there is a largely
uniform intensity of
illumination across the film section. The low contrast between the amount of
polarised light
transmitted through the tear susceptible line (907) and the rest of the BOPP
film (901) is
because the polymer chains within the line (907) and film (901) are aligned in
substantially the
same direction with respect to the plane of polarisation of the incident
polarised light.
Figure 11 is a photograph of the BOPP film of Example 1 herein. The photograph
was taken
under normal transmitted light and shows a cross-section through the film
(1001) sandwiched
within an embedding material (1023). A scale bar (1025) 50 microns in length
is superimposed
onto the photograph to indicate the degree of magnification of the image. This
photograph
shows that the film has only very slight almost non-existent ridges or furrows
at the surface of
the tear susceptible line (1007) and then mostly only on one surface, that
incident to the laser
beam.
Figure 12 is a photograph taken under polarised light of the same sample of
Example 1 at the
same magnification as in Figure 11. It can be seen that the orientation of
material within the
tear susceptible line (1107) is different to that within the rest of the film
(1101) as much less
polarised light is transmitted through the tear susceptible line (1107) which
appears almost
black. This high contrast is due to a greater degree of light scattering from
the polymer chains
within the tear susceptible line which are at a different angle to the plane
of polarisation of the
incident polarised light than the polymer chains in the rest of the film. Thus
when illuminated
under polarised light, the tear susceptible line (1107) is seen as much darker
when the rest of
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19
the BOPP film (1101) is bright (and vice versa).
Note when comparing features such as grooves and ridges the photographs of the
film of the
present invention (Figures 10 and 11) were taken at a higher (about twice)
magnification
compared to the photographs of the prior art film (Figures 8 and 9).
Measuring PP chain orientation within the line
The degree of polarisation of certain bands in a spectrum obtained using
polarised confocal
Raman microscopy can be used to indicate the direction of preferred
orientation within a
sample and compare relative orientations between regions of a sample. This
technique was
used to demonstrate differential orientation of polypropylene polymer within a
tear susceptible
line of the present invention prepared on a BOPP film analogously to those
examples
described herein.
One of the Raman bands is strongest when the Raman laser is polarised parallel
to the
extended chain director (the parallel band) and another is strongest when the
polymer chains
are aligned perpendicular to the laser polarisation (the perpendicular band).
There are many
bands in the Raman spectrum of polypropylene (PP) which can be used for this
purpose. The
Raman band is identified by wave number which is the number of cycles of a
wave in unit
length and is the reciprocal of the wavelength. An intensity ratio can be
measured which is the
intensity of a parallel band [= Ill(wavenumber)] divided by the intensity of a
perpendicular band
[= I-L(wavenumber)]. One can infer from a high value of the intensity ratio
that the polymer
chains are preferentially aligned towards the direction of polarisation of the
laser.
With reference to Figure 13 herein, a Raman polarised laser beam was focused
onto the
surface of a film of the present invention comprising a BOPP film onto which a
tear susceptible
line was formed analogously to the method of the invention described in
Example 1 herein.
The line was observed visually under the Raman. microscope to be about 25 to
30 microns
wide. A 50 times magnification objective lens was used to give a lateral
resolution of about 2
microns for the Raman laser beam. The relative intensity of a pair of bands in
the Raman
spectrum was me&sured whilst scanning the focus point of the Raman laser beam
at 3 micron
intervals along a track perpendicular to and across the tear susceptible line.
The Raman laser
beam was polarised parallel to the direction of this line.
The plot shown in Figure 13 was obtained where the ordinate denotes the
intensity ratio
III (815cm-1)/I-L(840cm"1) which is dimensionless and the abscissa denotes the
position of the
Raman laser along the scan track as a distance in microns (pm) with respect to
an arbitrary
starting point on the PP film adjacent the tear susceptible line. Differences
in polymer
orientation within this line compared to the rest of the film can be seen. A
higher intensity ratio
is consistent with PP chains which are more preferentially oriented in the
direction of the line.
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The shape of the profile in Figure 13 show that for this embodiment of a tear
susceptible line of
the present invention the orientation of PP chains is significantly higher
within the line than in
the surrounding film. The PP chains within the line are preferentially
oriented therealong
5 compared to PP in the rest of the film. Without wishing to be bound by any
mechanism, one
explanation may be because formation of a line with a laser as described in
the Examples
herein is at a power which is sufficiently low to be non ablative but
sufficiently high to anneal the,
film along the line and hence re-orient the PP chains. To confirm that an
optical artefact (e.g.
due to instrument dichroism) was not being observed, the experiment described
above was
10 repeated by rotating the film through 900 in the spectrometer whilst
keeping the laser
polarisation fixed. Similar results were observed.
